The present invention relates to a numerical control machining method used to carry out machining of workpieces by controlling a machine tool with the use of a numerical controller. More particularly, the invention relates to a numerical control machining method which achieves machining by controlling rotary tools with the use of a numerical controller.
In a conventional numerical control machining method, a machine tool is moved relative to a workpiece by instructions given in the form of numerical information. Accordingly, with the use of a numerically controlled machine tool, it is easily possible to machine workpieces of complicated configurations with a great accuracy, thereby attaining a high productivity.
Generally, a numerical control machining system is constructed as shown in FIG. 1. The system includes a numerical controller 120 for computing numerical control data in response to commands received from an external device through a terminal 110. A machine tool 130 is controlled by the numerical control data produced by the numerical controller 120. The numerical controller includes an input unit 121 for receiving commands from an external device, a processor unit 122 for processing the commands from the input unit 121, a memory unit 123 for storing the processed results from the processor unit 122 as well as commands from the input unit 121 and the like, a control unit 124 for controlling the operation of the processor unit 122, and an output unit 125 for outputting the processed information as instructions to directly control the machine tool 130. The machine tool 130 includes a rotary tool 131 mounted on a tool holder 132, with the tool holder 132 being received by the chuck of a spindle 133. The spindle 133 is rotated by motor 134, which is driven by a signal from the output unit 125 of the numerical controller 120. Further, a workpiece 140 is fixed on a table 135 by a jig or the like. In FIG. 1, reference numeral 136 indicates a lead or ball screw for moving the table 135 in the X-axis direction, with the lead screw 136 being driven by an X-axis feed motor 138 via a gear box 137. In turn, the X-axis feed motor 138 is driven by a signal from the output unit 125 of the numerical controller 120. Similarly to the arrangement where the table 135 is moved in the X-axis direction by the X-axis driving or feed motor 138 and the lead screw 135, there are provided mechanisms (not shown) for moving the table 135 in the Y- and Z-axis directions by signals from the numerical controller 120.
As mentioned above, the invention relates to a numerically controlled rotary-type machine tool. For convenience of explanation, it is assumed that a lathe is employed including a drill and a cutting tool.
FIG. 2 is a diagram showing a lathe of a type to which the invention can be applied. In FIG. 2, reference numeral 1 indicates a spindle assembly, 2 a chuck, 3 a workpiece, 4 a tool support, 5 a rotary tool or drill, and 6 a cutting tool.
To conduct a machining operation, the workpiece 3 is mounted with the chuck 2 at a predetermined position. The tool support 4 then selects, for instance, the rotary tool 5, after moving the rotary tool 5 into the appropriate position, so that the tip of the rotary tool 5 will meet a predetermined start point on the workpiece 3 when it is advanced. The tool 5 is rotated at a predetermined speed. The tool 5 is then moved forwardly by the tool support 4 to cut the workpiece 3. After the workpiece 3 has been drilled to a given depth, the tool support 4 is moved rearwardly, returning the rotary tool 5 to the machining start point, whereby one drilling operation has been completed.
If n holes a, b, . . . n are to be formed in the workpiece 3 at positions as shown in FIGS. 3a and 3b, a conventional numerically controlled system was typically operated in accordance with a machining program such as shown in FIG. 4. In this program, at step N1, a command T t1 t2 t3 t4 * is first employed to select the desired tool. Next, at N2, a command G50 X x1 Z z1 * is issued to select a work coordinate system for the tool. At step N3, a command M03 S s1 s2 s3 * is employed to designate the direction of rotation of the tool and the rate of rotation of the tool, and also to start the rotation of the tool. The following command of G00 X x2 Z z2 * at step N4 is utilized to position the workpiece to the predetermined machining start point. At N5, the command M m1 * positions the tool at a given rotational angle .theta..sub.0. Then, the command G77 X x3 Z z3 Dd Ff * at step N6 effects the start of the machining of the workpiece 3. In this step, x3 z3 indicates the coordinates of the terminal point, that is, the farthermost position of the tip of the rotary tool. The factor d indicates the amount of incremental movement of the tool support and rotary tool, and f the incremental speed of the tool.
Using the step described above, a machining operation for a first hole is completed. Next, the rotation/positioning command M m2 * at step N7 causes the workpiece 3 to be rotated through an angle of .theta..sub.1, thereby positioning the workpiece 3 so that the rotary tool will, when advanced, then be properly positioned to form the second hole. By repeating the drilling cycle command G77 . . . * at step N8 and the rotation/positioning command M m2 * and the steps there between, a total of n drilling operations is effected. Once the n drilling operations have been completed, at step N n3, a command G00 X x1 Z z1 M05 * is employed to return the tool 5 to its initial position, to stop the rotation of the tool, and to terminate the machining operation.
As is believed clear from the foregoing description, in the conventional machining method employing a conventional program, it is necessary to provide rotation-instructing and position-instructing commands for the workpiece 3 and the rotary tool 5 for each hole to be formed. Further, it is necessary to program the entire route of the tool, after fully considering the positional relationship between the workpiece 3 and the tool 5. Hence, a great deal of programming skill was required, and much time was needed to compile the operating program in such a conventional system.
Accordingly, it is an object of the present invention to provide a numerically controlled machining method in which the above-discussed drawbacks are eliminated.
More specifically, it is an object of the present invention to provide a numerical control machining method whereby plural drilling operations can be effected with a single machining command, which incorporate therein several rotation and positioning commands for the workpiece and for the drilling operation.
It is a further specific object of the invention to provide a numerical control machining method in which the machining program can be easily prepared, even by one having no particular programing skills.
A still further object of the invention is to provide a numerical control machining method which permits the machining operation to be completed within a shorter period of time than was possible with prior approaches.